1. Scope
The present invention relates to a novel process for removing sidewall residue after dry etching. The present invention also relates to a novel solution for removing sidewall residue after dry etching.
2. Current State of the Art
Processes of Integrated Circuit (IC) Manufacturing
First is deposited a layer of metal, such as Al, on a substrate surface, such as a wafer, then coating a layer of photoresist on it. This is followed by exposure, developing, etching, ion implantation and photoresist removing. Continuous cycles of film deposition, photoresist coating, exposure, developing, etching and removal of photoresist continue until the desired device is achieved.
There are two kinds of photoresist: positive type and negative type. For positive type photoresist, the area of exposure can be dissolved in developer solution. For negative type photoresist, the area of non-exposure can be dissolved in developer solution. The major composition of positive photoresist is resin, such as Novolac resin. The major composition of negative type photoresist is polyisoprene compound. Generally, baking the photoresist layer after exposure is necessary to make sure that cross-linking reaction is done.
After creating basic IC pattern and more sophisticated IC pattern is to be processed on the substrate, the photoresist and sidewall residue must be removed very efficiently and completely. That is by the use of a photoresist stripper, as in U.S. Pat. Nos. 4,917,122 and 4,963,342 described. In the etching process of VLSI (Very Large Scale Integrated) or ULSI (Ultra Large Scale Integrated) manufacturing, sidewall passivation formed after dry etching can achieve the anisotropic phenomena of etching process, as in J. L. Vossen, et al, J. Vac Sci. Technol. AL. 1453 (1983); J. H. Thomas, et al, Appl. Phys. Lett. 43, 859 (1983), D. Thomson, et al, Appl. Phys. Lett. 146, 1103 (1985), and J. M. E. Harper, et al, J. Electrochem. Soc. 128, 1077 (1981) described. While etching Poly-Si, according to the etching chemistry of Cl2 or HBr, oxygen is added to enhance anisotropic tendency and selectivity to oxide layer, as in I. Morimoto et al, Digest of papers, Microprocess 202 (1992) described. While etching Poly-Si layer using Cl2 as etching gas, silicon reacting with chlorine becomes silicon chloride. If oxygen exists, silicon chloride will be oxidized to silicon oxide, as in K. V. Guinn et al, J. Vac. Sci. Technol. B 13, 214 (1995) described. This silicon oxide is the so-called sidewall passivation, which can prevent isotropic etching. The sidewall passivation cannot be removed completely by conventional ozone ashing and hot sulfuric acid process. In the general process, wafers after treatment of ozone ashing and hot sulfuric acid still need to be immersed in diluted HF solution. The time of immersion cannot last too long to avoid attacking bottom oxide layer. Although the residue can be removed by special stripper, it is not convenient enough. Therefore the process of removing sidewall residue after dry etching should be improved.
The present invention relates to a novel solution in which a certain amount of fluorine-containing compound, preferably hydrogen fluoride and ammonium fluoride, is added into sulfuric acid. This solution can completely remove sidewall residue which is formed after dry etching.
The invention also relates to a novel process by which sidewall residue after dry etching can be completely removed by the above mentioned novel solution.